MAP Calculator (Mean Arterial Pressure)

This MAP calculator (Mean Arterial Pressure calculator) finds the average arterial blood pressure during a single cardiac cycle. Its value is derived from a patient's systolic and diastolic blood pressures. In this article, we provide you with a definition of MAP, the normal mean arterial pressure level, teach you how to calculate the mean arterial pressure, and present you a handy MAP equation that you can use for manual calculations, including pulse pressure calculation. You will also find out how to measure blood pressure, and finally, what are the risks of hypertension — a too high blood pressure.

If you are interested in cardiology, you should visit our QTc calculator. There you will find lots of information about ECG interpretation, QT prolongation, and dangerous arrhythmias.

The mean arterial pressure (MAP) is defined as an approximation of the time-weighted average for blood pressure in large system arteries during the cardiac cycle. It is directly related to the cardiac output.

To calculate the MAP, you need two values — you systolic and diastolic blood pressure. They are usually given in the form XX/YY, where XX is the systolic pressure, and YY is the diastolic. For example, a person with blood pressure 120/80 has SBP = 120 mmHg, and DBP = 80 mmHg. In the next paragraph, we will teach you how to measure blood pressure.

What exactly are systole and diastole? To put it simply, systole is the contraction phase in the human heart, when blood is pumped from the heart to circulation. During the diastole phase, also called the relaxation phase, the ventricles are filled with blood. Blood pressure is much higher during the systole than during the diastole.

Take a look at the illustration above. The diastole phase corresponds to two-thirds of the cardiac cycle, while the systole phase occupies only one-third. This is why MAP is not calculated as an arithmetic average, but rather as a weighted average.

Have you ever wondered how much blood your heart pumps in one minute, one month or one year? What order of magnitude can it be? Now, you can calculate it with a help of our cardiac output calculator!

There are a few ways to measure blood pressure. In this paragraph, we will cover only non-invasive methods of measuring blood pressure.

The fastest method to assess blood pressure is by palpation — detecting a pulse over patient's arteries. Although not very accurate, it is especially useful in emergencies: saving victims of car accidents, patients undergoing cardiac arrest, etc. It is assumed that when the systolic blood pressure of a patient is over 70 mmHg, the pulse should be palpable over carotid (on the neck), femoral (in the groin area) and radial (near the wrist) arteries. When the systolic blood pressure drops to > 50 mmHg, we can feel the pulse only over carotid and femoral arteries and with a pulse between 40–50 mmHg, just over carotid artery.

The most predominant method of measuring a patient's pulse by a doctor in a hospital setting, is by using a stethoscope and sphygmomanometer. The doctor puts a cuff of the sphygmomanometer around the patient’s arm and places the stethoscope over the brachial artery at elbow level. He inflates the cuff and then starts slowly releasing the air carefully observing the value of pressure inside the cuff indicated by the sphygmomanometer. When he begins to hear a characteristic whooshing-like sound, he writes down the currently reported pressure – this is the systolic blood pressure of the patient. The doctor continues to deflate the cuff until he stops to hear the pounding. At this moment sphygmomanometer indicates the diastolic blood pressure of the patient. The healthcare specialist is now ready to calculate the mean arterial pressure!

There is a medical phenomenon known as "white coat syndrome" (or white coat hypertension). Many patients fears being examined by a doctor and, during measurement, their blood pressure raises as a response to the stress they are feeling. This causes falsely high results of blood pressure test and can lead to unnecessary treatment. Below the final method of how to measure blood pressure eliminates this problem.

We are talking about oscillometry. You may have encountered when you visited your grandma. She put a cuff from a strange looking device around her arm, pushed some buttons and then waited stationary for a moment while the device buzzed. The device was a blood pressure monitor. In this method, blood pressure is estimated by detecting and analyzing the oscillation of the blood flow (the pulse) inside the brachial artery. The whole process is performed automatically. All you need to do is to remember to calibrate the device once in a while so it's functioning appropriately and able to obtain the correct results.

The normal blood pressure for a healthy adult should measure between 90 mmHg and 119 mmHg for systolic blood pressure and between 60 mmHg and 79 for diastolic blood pressure. We diagnose prehypertension when a patient has a systolic blood pressure between 120 mmHg and 139 mmHg. Lower than normal blood pressure is called hypotension, while higher than normal blood pressure — hypertension. We will talk about the risks of hypertension in the last paragraph of this article.

You can use the following mean arterial pressure formula:

MAP = 1/3 × SBP + 2/3 × DBP

where

• MAP is the mean arterial pressure,
• SBP is the systolic blood pressure, and
• DBP is the diastolic blood pressure.

That's it! Now you know how to calculate mean arterial pressure!

The formula accounts for the duration of the diastolic portion of the cardiac cycle — note the factor before the SBP and DBP. At a normal resting heart rate (check the target heart rate calculator), the systolic phase is twice as short - it means that the ventricles need twice as much time to fill with blood than to pump it out.

This relation can be different in patients with bradycardia or tachycardia. Such patients cardiac cycle is slightly different (the shape of the arterial pressure pulse becomes "narrower"), and the MAP is closer to the arithmetic mean of SBP and DBP. In these cases electronic circuitry or digital techniques are typically required to find the MAP.

It is generally believed that MAP levels should not fall below 60 mmHg to maintain adequate tissue perfusion. Patients with severe sepsis or septic shock should have their MAP levels kept at about 65 mmHg at all times.

The normal mean arterial pressure in healthy patients should be between 70 and 100 mmHg. The values should never exceed 160; such a result reflects excess cerebral blood flow and may result in raised intracranial pressures.

Pulse pressure is the difference between systolic blood pressure and diastolic blood pressure. The pulse pressure correlates to the volume of blood ejected during a contraction of the left ventricle of the heart to the aorta and other arteries. We call this amount of blood the stroke volume. The bigger the stroke volume is, the higher the value the pulse pressure reaches. Stroke volume increases for a number of reason, but the most common is exercise. The compliance of the aorta is, in turn, a factor that has a negative impact on pulse pressure. We define compliance as the ability to stretch in response to the pressure inside a vessel-like organ of our body. Let's give an example. Suppose that you are trying to inflate a balloon for your friend's birthday party. A balloon with high compliance would be easier to inflate (you wouldn't have to blow into it with as much force), than a balloon with low compliance.

Physiologically, the aorta is somewhat elastic, meaning it has high compliance. Because of that, our pulse pressure remains at a healthy level of around 40 mmHg. In some conditions, like atherosclerosis (narrowing and hardening of blood vessels due to formation of plaque) or aortic dissection (a state in which blood gets between layers of aortic wall), the aorta may become stiff. This increases the value of pulse pressure.

Other pathologies associated with an increased pulse pressure include:

• Fever.
• Aortic regurgitation — a leak in the aortic valve, causing an inversion of blood flow in the aorta during diastole.
• Anemia — a low level of hemoglobin (an oxygen-transporting protein present in the red cells).
• Pregnancy.
• Increased intracranial pressure — with symptoms of Cushing’s triad: high blood pressure, slow heartbeat (bradycardia), and irregular breathing.
• Endocarditis — an inflammation of the inner layer of the heart wall.
• Hyperthyroidism — excessive production of the thyroid hormone by the thyroid gland.

You can use the mean arterial pressure calculator to perform the pulse pressure calculation PP. Simply subtract the diastolic pressure from the systolic one:

PP = SBP - DBP

Let's calculate the MAP of a person with a blood pressure of 120/80.

1. Determine the SBP (systolic blood pressure). It is the first number — in this case, 120 mmHg.

2. Find the DBP (Diastolic blood pressure). It is the second number — here equal to 80 mmHg.

3. Input these numbers to the MAP equation:

   MAP = 120 × 1/3 + 80 × 2/3
MAP = 40 + 53.33
MAP = 93.33 mmHg

4. You can also perform the pulse pressure calculation by subtracting the DBP from the SBP:

   PP = SBP - DBP = 120 - 80 = 40 mmHg.

Mean arterial pressure is considered to be a better indicator of tissue perfusion than SBP precisely because it accounts for the difference between the duration of the diastole and systole parts of the cardiac cycle. Hence, it is typically monitored in cases of organ perfusion disorders. Some of these cases include:

• Septic shock — a state of insufficiently low blood pressure caused by a substantial inflammatory response due to an infection. Damaged organs, our immune response, and cytokines (signal molecules) all cause blood vessels to dilate (broadening), resulting in low blood pressure.
• Cardiac patients on vasodilator infusion, for example, nitroglycerine (GTN — glyceryl trinitrate) — one of the most used medicines for the treatment of angina (pain in the chest caused by a too-low oxygen supply for the heart), heart failure, and high blood pressure. Nitroglycerine is reduced in our body to a form of nitric oxide (NO), which is a strong vasodilator. Although helpful in many situations, glyceryl trinitrate has some side effects. It causes headaches and hypotension — too low blood pressure. To avoid the occurrence of such unpleasant or dangerous events, nitroglycerine and every other drug has to be dosed very carefully.
• Head injuries — damage to a specific region of a human brain — rostral ventrolateral medulla (RVLM), located in the brain stem, may cause pathologies of blood pressure. RVLM, through neural fibers of the autonomic nervous system, controls the speed of the heart rate, the force of its contraction and the level of contraction or dilation of arteries and veins. Even an increased intracranial pressure may manifest as the already mentioned Cushing’s triad: slow heartbeat, high mean arterial pressure and irregular breathing pattern. You can determine your patient's heart rate by merely looking at the results of his ECG test. Check our ECG heart rate calculator to find a tool that will do all the math for you! You will also learn some tips and tricks to quickly evaluate someones heartbeat all by yourself.
• Dissecting abdominal aneurysm — a surgery procedure in which a doctor cuts out a weaker segment of the abdominal aorta, thus preventing it from bursting. This can save the patient from bleeding to death!

Let's assume you have two patients, one with the blood pressure measurement 110/40 and the second with a pressure 90/65. Which blood pressure is better?

Intuitively, we concentrate on the first number — the systolic blood pressure. If it was the only indicator, we would say that the first patient has a better blood pressure. But what happens if we calculate MAP?

MAP1 = 110/3 + 40 × 2/3 = 63.33 mmHg

MAP2 = 90/3 + 65 × 2/3 = 73.33 mmHg

The mean arterial pressure of the first patient is much lower and hence worse. This example shows that diastolic pressure plays a vital role in determining the health condition of the patient.

Although we monitor the mean arterial pressure mainly for fear of it dropping too much, the majority of people should worry instead about having a too high blood pressure — hypertension. As we have already mentioned, blood pressure is considered high when the systolic blood pressure is equal to or above 140 mmHg and/or the diastolic blood pressure is equal to or above 90 mmHg.

Chronic hypertension leads to:

• Heart attack.
• Heart failure — when the heart is no longer able to pump blood against such high pressure in the arteries.
• Vessel damage — high blood pressure may create aneurysms, an outward balloon-like bulging in walls of arteries. This can lead to a bursting of artery and internal bleeding.
• Stroke.
• Kidney failure.
• Blindness.
• Cognitive impairment.

As you can see, the danger is real. We should do whatever we can to save ourselves from developing hypertension. We will give you several pieces of advice which will help you keep your blood pressure low.

You should routinely check your blood pressure, and, if it is high, consult a healthcare specialist. Luckily, there are also many ways, available for you right here and now, which can prevent and even treat hypertension.

• Maintaining a healthy diet: reducing salt and saturated fats intake, eating many fruits and vegetables.
• Avoiding alcohol and tobacco.
• Exercising and practicing sports — at least 30 minutes a day.
• Remaining calm and avoiding stress.

We wish you a healthy and high blood pressure free life with Omni Calculator!